OK, I'd checked for this before and found no sign that it's what was happening.
I suspected the top coat had just run off the body completely, but there was no drops on the board below where I hung it.
This time I caught it.
I think the reason the top coat isn't building up with multiple coats is that each coat running off.
That drop has gathered from runs all down the body joining across the bottom edge headed to the lowest point.
Maybe I need to do the front and back one at a time and let it cure laying flat.